The attempt of some Moscow writers to challenge Soviet thinking, yet careful nonpolitical journal called Metropol is faltering under the weight of an ambiguous, but steadily sharpening official counterattack aimed at splitting the group.

The sharpest blow has been dealt against Viktor Yerefeyev, a critic, and Yevgeny Popov, a Siberian writer. They are relatively unknown and thus most vulnerable to such presures. The Moscow Writers' Union has canceled their memberships, dampening their hopes of gaining success as literary figures within the official world of state publishing houses.

The writers' Union through its official journal, Moskovsky Literator, suggested their membership could be reconsidered once they had published books in their own right instead of the smaller collections of work that have appeared in literary journals. Such tactics suggest that the authorities are hopeful of avoiding an embarrassing showdown over Netropol by dispersing the group and ignoring their demands that the collection be published without undergoing censorship.

But, led by popular novelist and screenwriter Vasil Aksyonov, six of the 23 Metropol writers have threatened to resign from the Writers' Union if the two young men are not reinstated.The supporters of Popov and Yerefeyev include Bella Akhmadulina a poet, and novelists Fasil Iskandr and Andrei Bitov.

It is significant that their protective action on behalf of Yerefeyev and Popov has not been joined by Metropol's premier contributor, poet Andrei Voznesensky, who recently spent 10 days in the United States giving readings of his works.

This is the splitting of the Metropol group that the authorities clearly have sought, and that ultimately may spell the end of the censorship challenge.

Metropol, a collection of short stories, plays poetry, criticism and drawings, emerged in January in eight hand-produced copies containing about 250,000 words. The volumes included such direct challenges to censorship as explicit sexual scenes and were viewed as a bold attempt at loosening censorship.

Two copies have made their way to the West and a bound facismile copy already has been produced in the United States, with plans for an English version later this year. Establishment writers here scathingly attacked it as "poronography of the soul," in the words of their chief, Felix Kuznetsov.

Volznesensky's public inaction on behalf of Popov and Yerefeyev has sparked little detectable bitterness within the Moscow literary community.

Vozensensky declined to talk about the Metropol effort. But friends said he joined, offering several poems, in the belief that "the time is now" for attempts to loosen the censorship grip, as one quoted him. One source quoted him as asserting that in general, "The most reactionary moment today is better than the most liberal moment in the past."

Some Western specialists in Soviet literature believe that the very fact that the Metropol effort has not been met with crushing countermeasures indicates a loosening of the state's grip.

Nevertheless, as one Moscow writer described it last week, bouts with the unseen censor invariable are suffocating experiences.

"It is like tearing feathers from a chicken, what they do. You submit 200 poems and only 40 are found to have merit. Then, with the 40 in hand, you are asked, 'Why is this character a man? Why not make it a woman?' 'Why does this end in tears? Can't you give it a more positive ending?' Why is this one so pessimistic? This is an optimistic country.'"

"I didn't expect Andrei to join us, and in fact, I didn't ask him to," Aksyonov said in an interview. He said he understood and accepted the poet's need to stand aside just now.

Aksyonov has strengthened his own public gestures for the two by writing an additional open letter in their support that has been published in the West.

An outsider might argue that an open letter hardly adds up to forthright protest. But in the cat-and-mouse game of dealing with party bureaucrafts, bluff and show can sometimes be more effective than the grand gesture.

Aksyonov has never engaged in politics, but that he should press the Metropol issue seems in perfect keeping with his career.

A physician by training, he pursued a writer's career and became a literary sensation in 1961 with "Ticket to the Star" in which the daringly -- for the Soviet Union -- recreated coarse adolescent slang, portraying four teenagers' lives of bitter detachment from the "Soviet reality" of party controls and gross officials around them.

Although his vogue has faded among Soviet teen-agers today, their mothers and fathers remember him and the man who dared write about the stilyagi -- this literally translates as "stylies" the Soviet version of 1950s Teddy Boys, with their pegged plants, bright jackets and long hair.

In recent years, Aksyonov, 46, has begun writing for films and his most recent, entitled "While Our Dream Is Crazy," was awaited expectantly here early this year as one of the season's best comedies, a genre in short supply here.

Then came the Metropol scandal. The movie has been shelved, perhaps blighting the career of its young director, Yuri Gorkavenko.

Aksyonov says he draws sustenance from his 80-year-old father, Pavel, an old Bolshevik who was arrested in the 1937 Stalin purges and disappeared for 18 years in the Gulag Archipelago where millions died.

Aksyonov's father, who was mayor of Kazan in central Russia at the time of his arrest, now lives there in retirement and was recently awarded a medal by the government.

"He's a very stong, very clever man," say the son." He supports me in this."